Ofdm modulated wave transmitter apparatus, ofdm modulated wave transmission method, and program

ABSTRACT

In an orthogonal frequency division multiplex (OFDM) modulated wave transmitter apparatus, a symbol mapping circuit and a serial/parallel (S/P) converter generate an OFDM symbol signal from transmission data. An inverse fast Fourier transform (IFFT) circuit, a parallel/serial (P/S) converting and guard interval (GI) adding circuit, a timing adjusting circuit, a digital/analog (D/A) converter, a frequency converter, a local oscillator and an analog filter generate an OFDM modulated wave signal from the OFDM symbol signal. A power amplifier (PA) control circuit limits a band of the OFDM symbol signal and generates a PS control signal and a PA control signal. A PA designates a voltage supplied from a DC/DC converter as a PS voltage and amplifies and outputs the OFDM modulated wave signal based on the PA control signal.

TECHNICAL FIELD

The present invention relates to an orthogonal frequency divisionmultiplex (OFDM) modulated wave transmitter apparatus in which atransmission power amplifier (PA) is embedded, an OFDM modulated wavetransmission method, and a program.

BACKGROUND ART

An OFDM scheme uses a plurality of narrowband subcarriers and modulatesthe narrowband subcarriers to transmit a signal. Therefore, the OFDMscheme, whose frequency spectrum is close to a square shape as a whole,obtains high frequency utilization efficiency. In addition, the OFDMscheme is robust against a delayed wave because a symbol length is longas compared to a single carrier scheme. Further, the OFDM scheme can berobust within a multipath environment by adding a guard interval (GI).

In addition, in an orthogonal frequency division multiple access (OFDMA)scheme using the OFDM scheme, it is possible to simultaneously transmitinformation to a plurality of communication partners by allocatingsubcarriers to a plurality of information transmission destinations.

In an integrated services digital broadcasting-terrestrial (ISDB-T)scheme, which is a terrestrial digital television broadcasting scheme inJapan, a band segmented transmission-OFDM (BST-OFDM) scheme is adopted.In the BST-OFDM scheme, it is possible to select more appropriatesettings (a radio modulation scheme, transmission power, and the like)according to a purpose, by dividing subcarriers of the OFDM scheme intogroups called segment and allocating the segments to each purpose.

Further, in a long term evolution (LTE) system designed by ThirdGeneration Partnership Project (3GPP), the OFDMA scheme is adopted fordownlink from a base station to a mobile station and a singlecarrier-frequency division multiple access (SC-FDMA) scheme based ondiscrete Fourier transform (DFT)-spread OFDM is adopted for uplink fromthe mobile station to the base station.

In the SC-FDMA scheme based on the DFT-spread OFDM, a time waveform of asymbol sequence to be transmitted, is subjected to a DFT and thendesignated as an input of the OFDM scheme. Frequency components of thesymbol-sequence time waveform to be transmitted, which are DFT outputinput to OFDM, may be allocated to subcarriers indicated in advance fromthe base station in subcarrier mapping. The number of allocatedsubcarriers is set according to demand and not all subcarriers areconstantly allocated.

The OFDM scheme is multicarrier transmission comprised by manysubcarriers. An OFDM signal, which is an output of the OFDM scheme, hashigh peak power when peak values of subcarriers overlap. An example of abaseband OFDM signal waveform is illustrated in FIG. 6. When the OFDMsignal as described above is input to a PA having non-linearitycharacteristics, undesirable characteristic degradation, such asdegradation of transmission characteristics or the increase ofout-of-band radiation, is caused. Therefore, a PA having low non-lineardistortion characteristics is needed for an OFDM modulated wavetransmitter apparatus.

Generally, in case of a comparison under the same output power, anamplifier having higher saturation output power characteristics haslower non-linear distortion characteristics. However, the amplifier asdescribed above is not preferable in terms of the power efficiencybecause power consumption is high during a small signal of whichnon-linear distortion is not problematic. Consequently, it is necessaryto improve the non-linear distort on characteristics without degradingthe power efficiency.

To reduce the non-linear distortion in OFDM, a scheme of improvinglinearity during peak power generation is proposed, for example, inPatent Document 1. In the scheme of improving the linearity during thepeak power generation, the linearity is improved by temporarily applyinga high voltage or a large current to the PA when high peak power isgenerated. This scheme can improve transmission characteristics andout-of-band radiation characteristics of an OFDM signal in a range notexceeding a maximum rating of a component of a high-power amplifier anda range that does not adversely affect reliability.

DOCUMENTS OF THE PRIOR ART Patent Documents

[Patent Document 1] Japanese Unexamined Patent Application, FirstPublication, No. 2001-292034

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

However, there are the following problems in the scheme of improving thelinearity during the peak power generation according to Patent Document1 described above.

The first problem is that a circuit scale increases. This is because itis necessary to additionally provide an analog/digital (A/D) conversioncircuit, which performs A/D conversion again of an analog signal, towhich concerted once from an OFDM signal generated by digital signalprocessing, and the result of the A/D conversion is used for control.

The second problem is that a circuit is weak against noise andinterference from the environment. This is because an analog circuit,which is weak against noise as compared to a digital circuit, is used toperform the A/D conversion again of an analog signal, to which convertedfrom an OFDM signal generated by digital signal processing, and theresult of the A/D conversion is used for control. In particular, becausethe power of an output of a transmitter is usually high, it is necessaryto take measures so that the output does not cause interference.

Accordingly, it is preferable that the OFDM signal generated by digitalsignal processing is processed as a digital signal.

The third problem is that power consumption is large when the OFDMsignal has been processed as the digital signal. This is because thepower consumption is increased due to the use of many digital arithmeticoperations. In particular, there is a problem in that the powerefficiency is not improved in a scheme in which states of use ofsubcarriers are non-uniform, as the BST-OFDM scheme or the SC-FDMAscheme based on DFT-spread OFDM. This is because, when the states of useof the subcarriers are on-uniform, a state of use of each subcarrier isnot identified so that it is impossible to process suitably for a stateof use of an individual subcarrier and, as a result, power consumptionis not reduced.

The fourth problem is a cost increase caused by an increase of circuitscale, taking measures against noise and interference, and an increaseof power consumption as described above.

The present invention has been made in view of such circumstances, andan object of the invention is to provide an OFDM modulated wavetransmitter apparatus, an OFDM modulated wave transmission method, and aprogram, which can reduce a circuit scale, be robust against noise andinterference from the environment, reduce power consumption, and beimplemented at a low cost.

Means for Solving the Problems

According to the present invention for solving the above-describedproblems, there is provided an OFDM modulated wave transmitter apparatusincluding: an OFDM symbol signal generating circuit for generating anOFDM symbol signal from transmission data; an OFDM signal generatingcircuit for generating an OFDM modulated wave signal from the OFDMsymbol signal; a control circuit for generating a power supply (PS)control signal and a PA control signal from the OFDM symbol signal; aconverter for controlling an output voltage of a PS based on the PScontrol signal generated by the control circuit; and an amplifier foramplifying and outputting the OFDM modulated wave signal generated bythe OFDM signal generating circuit based on at least one of the outputvoltage controlled by the converter and the PA control signal generatedby the control circuit.

In addition, according to the present invention, there is provided anOFDM modulated wave transmission method including: a first step ofgenerating an OFDM symbol signal from transmission data; a second stepof generating an OFDM modulated wave signal from the OFDM symbol signal;a third step of generating a PS control signal and a PA control signalfrom the OFDM symbol signal; a fourth step of controlling an outputvoltage of a PS based on the PS control signal; and a fifth step ofamplifying and outputting the OFDM modulated wave signal based on atleast one of the controlled output voltage and the PA control signal.

In addition, according to the present invention, there is provided aprogram for causing a computer for controlling an OFDM modulated wavetransmitter apparatus to execute: an OFDM symbol signal generatingfunction of generating an OFDM symbol signal from transmission data; anOFDM signal generating function of generating an OFDM modulated wavesignal from the OFDM symbol signal; a control function of generating aPS control signal and a PA control signal from the OFDM symbol signal; aconverting function of controlling an output voltage of a PS based onthe PS control signal; and an amplifying function of amplifying andoutputting the OFDM modulated wave signal based on at least one of thecontrolled output voltage and the PA control signal.

Effect of the Invention

According to the present invention, it is possible to reduce anarithmetic operation amount and a circuit scale necessary for anarithmetic operation and hence reduce power consumption by employing adigital circuit, which is added to improve the power efficiency andnon-linear distortion of an amplifier and increases resistance againstnoise and interference, and cutting down a digital arithmetic operation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an OFDM modulated wavetransmitter apparatus according to a first embodiment of the presentinvention.

FIG. 2 is a block diagram illustrating a modified example according tothe first embodiment of the present invention.

FIG. 3 is a block diagram illustrating an OFDM modulated wavetransmitter apparatus according to a second embodiment of the presentinvention.

FIG. 4 is a block diagram illustrating an OFDM modulated wavetransmitter apparatus according to a third embodiment of the presentinvention.

FIG. 5 is a block diagram illustrating an OFDM modulated wavetransmitter apparatus according to a fourth embodiment of the presentinvention.

FIG. 6 is a conceptual diagram illustrating an OFDM baseband signalwaveform in an OFDM modulated wave transmitter apparatus.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Hereinafter, the embodiments of the present invention will be describedwith reference to the drawings.

First Embodiment

FIG. 1 is a block diagram illustrating an OFDM modulated wavetransmitter apparatus according to the first embodiment of the presentinvention. In the drawing, the OFDM modulated wave transmitter apparatus100 includes a symbol mapping circuit (Symbol Mapper) 101, aserial/parallel (S/P) converter 102, an inverse fast Fourier transform(IFFT) circuit 103, a parallel/serial (P/S) converting and GI addingcircuit 104, a timing adjusting circuit (Timing) 106, a digital/analog(D/A) converter 107, a frequency converter (Mixer) 108, a localoscillator (LO OSC) 109, an analog filter (band-pass filter (BPF)) 110,a power amplifier (PA) 111, a PA control circuit (control circuit)(CONT) 111, a power supply (PS) 115, and a DC/DC converter (DC/DC) 116.The OFDM modulated wave transmitter apparatus according to thisembodiment includes an OFDM symbol signal generating circuit having thesymbol mapping circuit 101 and the S/P converter 102 and an OFDM signalgenerating circuit having the IFFT circuit 103, the P/S converting andGI adding circuit 104, the timing adjusting circuit 106, the D/Aconverter 107, the frequency converter 108, the local oscillator 109,and the analog filter 110.

The PA control circuit (control circuit) 114 includes an IFFT circuit112, a P/S converting and GI adding circuit 113, a digital filter (BPF)121, a real component extraction circuit (Real) 122, an amplitudedetecting circuit (Amplitude Detector) 123, a control signal convertingcircuit (Comparator & Table) 124, and timing adjusting circuits 125 and126.

The symbol mapping circuit 101 receives a bit sequence includingtransmission data, and outputs a symbol of each OFDM subcarrier to theS/P converter 102. Each symbol corresponds to a combination of amplitudeand phase on a phase plane in one-to-one correspondence. The S/Pconverter 102 receives the symbol of each OFDM subcarrier and outputs aparallel conversion output to the IFFT circuits 103 and 112.

The IFFT circuit 103 receives the symbol of each OFDM subcarriersubjected to parallel conversion, transforms the symbol according to anIFFT, and outputs the transformed symbol. The P/S converting and GIadding circuit 104 receives an IFFT output from the IFFT circuit 103,and outputs a complex digital baseband signal, which is a complexnumber.

The timing adjusting circuit 106 receives the complex digital basebanddelays the received complex digital baseband signal by a predeterminedtime, and outputs the delayed complex digital baseband signal. The D/Aconverter 107 receives the complex digital baseband signal, which is theoutput of the timing adjusting circuit 106, and outputs a complex analogbaseband signal having an in-phase signal (I signal) and a quadraturesignal (Q signal).

The frequency converter 108 receives the complex analog baseband signaland a local oscillation signal, which is an output of the localoscillator 109, and generates a carrier-band OFDM signal. The analogfilter 110 receives the carrier-band OFDM signal from the frequencyconverter 108, removes an undesired wave, and outputs a removal resultto the PA 111.

On the other hand, the parallel conversion output from the S/P converter102 is input to the IFFT circuit 112 of the PA control circuit 114. TheIFFT circuit 112 receives the parallel conversion output, and outputscomplex time waveform data for PA control by performing the IFFT. TheP/S converting and GI adding circuit 113 receives an IFFT output fromthe IFFT circuit 112, and outputs ts a complex digital baseband signalfor PA control, which is a complex number.

The digital filter 121 receives the complex digital baseband signal forPA control, removes a component in an unnecessary band, and outputs aremoval result. The real component extracting circuit 122 receives thecomplex digital baseband signal for PA control, which is the output ofthe digital filter 121, and outputs a real digital baseband signal forPA control, which is a real component. The amplitude detecting circuit123 receives the real digital baseband signal for PA control, andoutputs an amplitude signal.

The control signal converting circuit 124 receives the amplitude signal,and generates and outputs a PS control signal and a PA control signal.The timing adjusting circuit 125 receives the PS control signal, delaysthe received PS control signal by a predetermined time, and outputs thedelayed PS control signal. The timing adjusting circuit 126 receives thePA control signal, delays the received PA control signal by apredetermined time, and outputs the delayed PA control signal. The DC/DCconverter 116 receives the PS control signal from the timing adjustingcircuit 125, converts a PS voltage from the PS 115 based on the PScontrol signal, and outputs voltage converted power to the PA 111.

The PA 111 receives the carrier-band OFDM signal from the analog filter110, the PA control signal from the timing adjusting circuit 126, andthe voltage converted power front the DC/DC converter 116, and outputsan amplified carrier-band OFDM signal.

Next, an operation of the first embodiment will be described.

A bit sequence including transmission data, when input to the OFDMmodulated wave transmitter apparatus 100, is input to the symbol mappingcircuit 101. In OFDM, data transmission is preformed by digitalmodulation on a plurality of subcarriers, respectively. The digitalmodulation is used to perform transmission by associating data with adiscrete position (symbol point) on the phase plane.

For example, according to a quadrature phase shift keying (QPSK)modulation scheme, two-bit information is transmitted in one symbolbecause four symbol points are defined and identified. Likewise,according to a 64 quadrature amplitude modulation (64 QAM) modulationscheme, 64 symbol points are defined and six-bit information istransmitted in one symbol. An operation of associating data to betransmitted with the symbol points, in other words, discrete positioncoordinates on the phase plane corresponding to the symbol points, isreferred to as mapping.

The symbol mapping circuit 101 distributes the bit sequence includingthe input transmission data to subcarriers, farther performs mapping toa symbol point of each subcarrier, and outputs a mapping result.Therefore, an output of the symbol mapping circuit 101 includes asubcarrier frequency and symbol point information associated with eachsubcarrier. The symbol point information is given as discrete amplitudeand phase in a polar coordinate model. The symbol point information isgiven as coordinate values of discrete in-phase and quadraturecomponents in an orthogonal coordinate model. Single-symbol pointinformation is referred to as a complex symbol.

Here, in an example of the orthogonal coordinate model, a complex symbold_(n) for modulating an n^(th) subcarrier is defined by the followingExpression (1). In addition, j denotes an imaginary unit.

d _(n) =a _(n) +jb _(n) (n=0, . . . , N−1)   (1)

The S/P converter 102 converts an output of the symbol mapping circuit101, which is time-series data, into parallel data for which the IFFTcircuit 103 can perform an IFFT. Here, serial-to-parallel conversion isperformed for the complex symbol d_(n). This is also subcarrierallocation related to the IFFT.

The complex symbol d_(n), subjected to parallel conversion and allocatedto each subcarrier of OFDM, is subjected to the IFFT by the IFFT circuit103, and output as complex time waveform data u{k/(Nf₀)} (where k=0, 1,2, . . . , N−1), which is parallel data. The complex time waveform datau{k/(Nf₀)} is expressed by the following Expression (2).

$\begin{matrix}{{{u( \frac{k}{{Nf}_{0}} )} = {\sum\limits_{n = 0}^{N - 1}\; {d_{n}( ^{j\frac{2\; \pi}{N}} )}^{nk}}}( {{k = 0},1,2,\ldots \mspace{14mu},{N - 1}} )} & (2)\end{matrix}$

The P/S converting and GI adding circuit 104 adds GI data to the complextime waveform data u{k/(Nf₀)}, which is the output of the IFFT circuit103, and further converts the complex time waveform data u{k/(Nf₀)} withthe GI data into serial time-series data. The serial time-series data isoutput as a complex digital baseband signal, which is a complex number.A section of k=0 to N−1 in Expression (2) is a time length of one symbolin OFDM, which is referred to as an OFDM symbol. A GI is a time intervalprovided between OFDM symbols in order to prevent interference ofdelayed waves. A GI is generally allocated at the head of an OFDMsymbol, and filled with the OFDM symbol tail waveform of an equal timelength.

The timing adjusting circuit 106 delays the complex digital basebandsignal by a predetermined time, and outputs the delayed complex digitalbaseband signal. The PA 111 is controlled by the PA control circuit 114.

On the other hand, the carrier-hand OFDM signal should be input to thePA 111 after control setting of the PA 111 has been completed, and isdelayed by the timing adjusting circuit 106 to compensate for a delaytime of the PA control circuit 114.

The D/A converter 107 receives a complex digital baseband signal, whichis an output of the timing adjusting circuit 106, and outputs a complexanalog baseband signal, which is an analog waveform having an in-phasesignal (I signal) S_(I)(t) and a quadrature signal (Q signal) S_(Q)(t)expressed by the following Expressions (3) and (4).

$\begin{matrix}{{s_{I}(t)} = {\sum\limits_{n = 0}^{N - 1}\; \{ {{a_{n}{\cos ( {2\; \pi \; {nf}_{0}t} )}} - {b_{n}{\sin ( {2\; \pi \; {nf}_{0}t} )}}} \}}} & (3) \\{{s_{Q}(t)} = {\sum\limits_{n = 0}^{N - 1}\; \{ {{a_{n}{\sin ( {2\; \pi \; {nf}_{0}t} )}} + {b_{n}{\cos ( {2\; \pi \; {nf}_{0}t} )}}} \}}} & (4)\end{matrix}$

The frequency converter 108 mixes the in-phase signal (I signal)S_(I)(t) and the quadrature signal (Q signal) S_(Q)(t), which arecomprised in the complex analog baseband signal, with a localoscillation signal as a carrier wave, which is an output of the localoscillator 109, cancels image component, and converts input signals intoa carrier-band OFDM signal S(t) expressed by the following Expression(5) at last.

$\begin{matrix}{{s(t)} = {\sum\limits_{n = 0}^{N - 1}\; \lbrack {{a_{n}\cos \{ {2\; {\pi ( {f_{c} + {nf}_{0}} )}t} \}} - {b_{n}\sin \{ {2\; {\pi ( {f_{c} + {nf}_{0}} )}t} \}}} \rbrack}} & (5)\end{matrix}$

The analog filter 110 removes an undesired wave from the carrier-bandOFDM signal from the frequency converter 108, and outputs a removalresult to the PA 111.

On the other hand, symbol point information of each subcarrier of OFDM,which is subjected to parallel conversion by the S/P converter 102, isalso input to the PA control circuit 114. A complex symbol input to thePA control circuit 114 becomes c_(n) (n=0, . . . , N−1).

The IFFT circuit 112 transforms the parallel conversion output of theS/P converter 102, which is input to the PA control circuit 114,according to the IFFT, and outputs complex time waveform data for PAcontrol v{k/(Nf₀)} (where k=0, 1, 2, . . . , N−1), which is paralleldata, expressed by the following Expression (6).

$\begin{matrix}{{{v( \frac{k}{{Nf}_{0}} )} = {\sum\limits_{n = 0}^{N - 1}\; {c_{n}( ^{j\frac{2\; \pi}{N}} )}^{nk}}}( {{k = 0},1,2,\ldots \mspace{14mu},{N - 1}} )} & (6)\end{matrix}$

Here, the complex symbol c, corresponds to the complex symbol d_(n), thecomplex time waveform data for PS control v{k/(Nf₀)}; (where k=0, 1, 2,. . . , N−1) corresponds to complex time waveform data u{k/(Nf₀)}, andthe numbers of data are equal. However, the PA control does not needarithmetic precision as signal generation. Therefore, c and v{k/(Nf₀)}allow to decrease the effective number of digits in the arithmeticoperation as compared to d_(n) and u{k/(Nf₀)}, so that a scale of anarithmetic operation circuit and an arithmetic processing amount can bedecreased. Consequently, it is possible to speed up an arithmeticoperation, reduce power consumption, and lower cost.

The P/S converting and GI waveform adding circuit 113 adds GI data tothe complex time waveform data for PA control v{k/(Nf₀)}, which is theoutput of the IFFT circuit 112, further converts the addition resultinto serial time-series data, and outputs a complex digital basebandsignal for PA control, which is a complex number. The digital filter 121extracts a required band from the complex digital baseband signal for PAcontrol, and outputs an extraction result.

A broadband circuit having a control band from a lowest subcarrierfrequency or less to a highest subcarrier frequency or more is necessaryfor the PA control circuit 114 if the PA control circuit 114 is neededto provide the PA 111 with a PS voltage and a PA control signal byfollowing all subcarriers. The broadband operation causes an increase incircuit scale and an increase in power consumption according to anincrease in an arithmetic operation amount in digital processing, and ademand of a broadband analog circuit and an increase in powerconsumption in analog processing, further leading to an increase incost.

On the other hand, in the OFDM scheme, as described above, it ispossible to set a radio modulation scheme and transmission power foreach subcarrier or each subcarrier segment, or to use only somesubcarriers. It is possible to reduce an arithmetic operation amount ofdigital processing and introduce a cheap analog processing system with anarrow band and suppress power consumption and circuit cost if theabove-described control band can he set only for a frequency band of asubcarrier segment set to a multi-valued radio modulation scheme, whichis susceptible to the non-linear distortion by the amplifier, or highpower, which is dominant in occurrence of non-linear distortion, orexactly used subcarriers.

In this first embodiment, it is possible to obtain the above-describedadvantageous effects by installing the digital filter 121 and limitingthe control band.

In addition, the symbol mapping circuit 101 preferentially allocates asubcarrier segment set to a multi-valued radio modulation scheme, whichis susceptible to the non-linear distortion by the amplifier, or thehigh power, which is dominant in the occurrence of non-lineardistortion, or subcarriers to be exactly used to low-frequencysubcarriers, so that an operation speed of the PA control circuit 114 isdecreased. Further, it is possible to reduce the arithmetic operationamount and configure a low-speed circuit by fixing allocation tolow-frequency subcarriers. As a result, it is possible to suppress powerconsumption and circuit cost. These are also some improvements obtainedby the band limitation.

The real component extracting circuit 122 extracts a real component froma digital baseband signal for PA control, which is the output of thedigital filter 121, and outputs a real digital baseband signal for PAcontrol. The amplitude detecting circuit 123 obtains the amplitude ofthe real baseband signal for PA control, and converts the amplitude intoan amplitude signal. There is a method of obtaining an absolute value asa method of detecting the amplitude. The amplitude signal is input tothe control signal converting circuit 124, and converted into a PScontrol signal and a PA control signal.

The timing adjusting circuit 125 delays the PS control signal by apredetermined time so as to compensate for response delay of the DC/DCconverter 116, and inputs the delayed PS control signal to the DC/DCconverter 116. The DC/DC converter 116 provides a voltage based on thePS control signal to the PA 111. On the other hand, the timing adjustingcircuit 126 delays the PA control signal by a predetermined time so asto compensate for response delay of the PA 111, and provides the delayedPA control signal to the PA 111.

The PA 111 amplifies and outputs the carrier-band OFDM signal from theanalog filter 110 with the voltage supplied from the DC/DC converter 116as a PS voltage, setting an internal bias current and voltage based onthe PA control signal.

The amplitude signal indicates the amplitude of the carrier-band OFDMsignal to be amplified by the PA 111. When the amplitude of the OFDMsignal is large, the DC/DC converter 116 is controlled according to thePS control signal so that a high voltage is provided. As a result, it ispossible to suppress the generation of non-linear distortion even duringpeak power. In addition, the internal bias current or voltage of the PA111 is controlled according to the PA control signal so that thenon-linear distortion generation is suppressed. Specifically, if anamplifier device is a bipolar transistor, a collector current iscontrolled by a base current control. If the amplifier device is afield-effect transistor, a drain current is controlled by a gate voltagecontrol. When non-linear distortion is desired to be suppressed, onecontrol method is a method of increasing a collector current or a draincurrent when no signal is input.

On the other hand, when the amplitude of the OFDM signal is small, thepower efficiency of utilization is high in the case in which the voltagesupplied from the DC/DC converter 116 to the PA 111 is low or the casein which a current flowing through a transistor or the like inside thePA 111 is set to be small. Consequently, the PS control signal and thePA control signal can be controlled to satisfy the above.

The above-described generation of the PS control signal and the PAcontrol signal based on the amplitude signal by the control signalconverting circuit 124 can be performed based on a preset conversiontable, a function expression, or both. In addition, the conversion tablemay be also used with an interpolation or extrapolation calculationbased on the table values.

There is delay in each of output voltage control of the DC/DC converter116 and bias control in the PA 111. In addition, it is preferable thatcontrol be performed with hysteresis so that non-linear distortionsuppression control is initiated before the transition from smallamplitude to large amplitude of an amplified signal, and reversely isended with delay after the transition from large amplitude to smallamplitude. The control signal converting circuit 124 and the timingadjusting circuits 125 and 126 cooperatively perform hysteresis control.Specifically, the control signal converting circuit 124 shares a processof extending a period in which non-linear distortion is suppressed, andthe timing adjusting circuits 125 and 126 implement hysteresis controlcorresponding to a transition direction of the signal amplitude byabsorbing a delay characteristic difference.

In the SC-FDMA scheme based on DFT-spread OFDM, “DFT-subcarrier mappingcircuits,” that is, a DFT circuit 130 and a subcarrier mapping circuit131, are interposed between the S/P converter 102 and the IFFT circuits103 and 112 as illustrated in FIG. 2. In this case, the sameadvantageous effects as described above are also obtained.

According to the above-described first embodiment, based on the OFDMsymbol signal, the IFFT circuit 103, the P/S converting and GI addingcircuit 104, the timing adjusting circuit 106, the D/A converter 107,the frequency converter 108, the local oscillator 109, and the analogfilter 110 generate an OFDM modulated wave signal, and the PA controlcircuit 114, the PS 115, and the DC/DC converter 116 generate powerhaving a predetermined voltage and a PA control signal. Consequently, itis possible that each signal is generated by calculation under thenumber of significant digits suitable for the signal, so that the scaleof an arithmetic operation circuit and an arithmetic processing amountare decreased. As a result, it is possible to speed up an arithmeticoperation and reduce power consumption.

In addition, because the digital filter 121 is provided and a controlband of a control signal (a PS control signal and a PA control signal)is limited, power consumption and circuit cost can be suppressed.

In addition, the symbol mapping circuit 101 preferentially allocates asubcarrier segment set to a multi-valued radio modulation scheme, whichis susceptible to the non-linear distortion by the amplifier, or thepower, which is dominant in the occurrence of non-linear distortion, orsubcarriers to be exactly used to low-frequency subcarriers, so that anoperation speed of the PA control circuit 114 is decreased. Further, itis possible to reduce the arithmetic operation amount and configure alow-speed circuit by fixing allocation to low-frequency subcarriers. Asa result, it is possible to suppress power consumption and circuit cost.

Further, because the input of the PA control circuit 114 is a digitalsignal, it is possible to reduce the effect of noise and interferencefrom the environment.

Second Embodiment

Next, the second embodiment of the present invention will be described.

Although a basic configuration of this second embodiment is the same asthat of the first embodiment, a technique for generating a PA controlsignal is further provided in the second embodiment.

FIG. 3 is a block diagram illustrating an OFDM modulated wavetransmitter apparatus according to this second embodiment. Partscorresponding to FIG. 1 are denoted by the same reference numerals, anddescription thereof is omitted. In this second embodiment, an IFFTcircuit 212 and a PA control circuit (control circuit) 214 are providedinstead of the IFFT circuit 112 and the PA control circuit 114 of theOFDM modulated wave transmitter apparatus 100 of FIG. 1, respectively.In addition, the digital filter 121 is omitted.

The S/P converter 102 receives a complex symbol of each subcarrier ofOFDM and outputs a parallel conversion output to the IFFT circuits 103and 212. The IFFT circuit 212 receives the parallel conversion output,selects part of the parallel conversion output by a selection circuit(not illustrated) included therein, and outputs complex time waveformdata for PA control generated by performing an IFFT to the selectedpart. The P/S converting and GI adding circuit 113 receives an IFFToutput from the IFFT circuit 212, and outputs a complex digital basebandsignal for PA control, which is a complex number. The real componentextracting circuit 122 receives the complex digital baseband signal forPA control, which is the output of the P/S converting and GI addingcircuit 113, and outputs a real digital baseband signal for PA control,which is a real component.

Next, operations different from those of the OFDM modulated wavetransmitter apparatus 100 of the first embodiment, among operations ofthe OFDM modulated wave transmitter apparatus 200 illustrated in FIG. 3,will be described.

The parallel conversion output of the S/P converter 102 is as shown inExpression (1). In Expression (1), n denotes each subcarrier. In theIFFT circuit 212, an arithmetic operation is performed only for complexsymbols of subcarriers necessary for PA control, and complex symbols ofother subcarriers are handled as 0.

Hereinafter, the case in which symbol information of m_(s) ^(th) tom_(e) ^(th) (0≦m_(s)<m_(e)≦N−1) subcarriers is selected, is shown. Aninput c_(m) (m=0, . . . , N−1) of the IFFT circuit 212 is expressed bythe following Expressions (7) and (8).

c _(m) =a _(m) +jb _(m) (m=m _(s) ,m _(s)+1, . . . , m _(e)−1,m _(e))  (7)

c _(m)=0 (m=0, . . . , m _(s)−1,m _(e)+1, . . . , N−1)   (8)

The IFFT circuit 212 performs an IFFT, and outputs complex time waveformdata for PA control w{k/(Nf₀)} (where k=0, 1, 2, . . . , N−1), which isparallel data.

$\begin{matrix}{\begin{matrix}{{w( \frac{k}{{Nf}_{0}} )} = {\sum\limits_{n = 0}^{N - 1}\; {c_{n}( ^{j\frac{2\; \pi}{N}} )}^{nk}}} \\{= {\sum\limits_{n = m_{s}}^{m_{e}}\; {d_{n}( ^{j\frac{2\; \pi}{N}} )}^{nk}}}\end{matrix}( {{k = 0},1,2,\ldots \mspace{14mu},{N - 1}} )} & (9)\end{matrix}$

When the above-described Expression (9) is compared to Expression (6),it can be seen that an arithmetic operation amount is obviously reducedfrom a difference of an addition range. In addition, the selection ofcomplex symbols of subcarriers shown in Expressions (7) and (8) limitssubcarriers required for the arithmetic operation, and also limits aband of complex time waveform data for PA control w{k/(Nf₀)} output bythe IFFT. Consequently, the same advantageous effects as those of thedigital filter 121 in FIG. 1 are obtained. Further, in this secondembodiment, it is possible to more flexibly obtain filter effectssuitable for use of an OFDM signal because a filter can be set for eachsubcarrier. Although the case in which continuous (adjacent) subcarriersin frequency are selected in the above-described example has been shown,discontinuous subcarriers may be selected.

In addition, when 0 is substituted into the input c_(m) of the IFFTcircuit 212, it is possible to suppress an arithmetic operation amountand hence suppress power consumption by performing a process ofbypassing a calculation path in which the multiplication of 0 occurs inan arithmetic operation of the IFFT circuit (in general, a butterflycalculation is well-known), instead of performing an arithmeticoperation of simply substituting 0 as arithmetic data. In addition, whensubcarriers to be used are fixed to some frequencies, it is possible toreduce a circuit scale by omitting an arithmetic operator correspondingto unused subcarriers in a circuit.

The selection of complex symbols of subcarriers can be performed by anoutput circuit to the IFFT circuit 212 within the S/P converter 102 aswell as by providing a selection circuit within the IFFT circuit 212.Further, because an object of PA control is to compensate for non-lineardistortion of a carrier-band OFDM signal, a baseband signal used forcompensation can be generated with shifting a subcarrier frequency to alowest frequency as shown in Expressions (10) and (11).

c _(n) =a _(m) +jb _(m) (n=m−m _(s) ,m=m _(s) ,m _(s)+1, . . . , m_(e)−1,m _(e))   (10)

c _(n)=0 (n=m _(e) −m _(s)+1, . . . , N−1)   (11)

As a result, it is possible to further decrease a control frequencyband, leading to the reduction of an arithmetic operation amount ofdigital processing and the introduction of a low-speed analog processingsystem.

According to the above-described second embodiment, it is possible tolimit the control frequency band even when there is no BPF 121 becausethe PA control circuit 214 generates a control signal by selectivelyreceiving a part of the OFDM symbol signal. As a result, it is possibleto suppress an arithmetic operation amount and the cost of an analogcircuit and further suppress the circuit scale and power consumption.

In addition, according to this second embodiment, a baseband signal tobe used for compensation can be generated with shifting a subcarrierfrequency to a lowest frequency. As a result, it is possible to furtherdecrease a control frequency band, reduce an arithmetic operation amountof digital processing, and introduce a low-speed analog processingsystem.

Third Embodiment

Next, the third embodiment of the present invention will be described.

Although a basic configuration of this third embodiment is the same asthat of the first embodiment, a different technique for generating a PAcontrol signal is further provided in the third embodiment.

FIG. 4 is a block diagram illustrating an OFDM modulated wavetransmitter apparatus according to this third embodiment. Partscorresponding to FIG. 1 are denoted by the same reference numerals anddescription thereof is omitted. In this third embodiment, a P/Sconverting and GI adding circuit 313 and a PA control circuit (controlcircuit) 314 are provided instead of the P/S converting and GI addingcircuit 113 and the PA control circuit 114 of the OFDM modulated wavetransmitter apparatus 100 of FIG. 1, respectively. In addition, the IFFTcircuit 112 is omitted.

The IFFT circuit 103 outputs complex time waveform data, which is anIFFT output, to the P/S converting and GI adding circuits 104 and 313.The P/S converting and GI adding circuit 313 receives the complex timewaveform data from the IFFT circuit 103, and outputs a complex digitalbaseband signal for PA control, which is a complex number, to thedigital filter 121.

Next, operations different from those of the first and secondembodiments, among operations of the OFDM modulated wave transmitterapparatus 300 illustrated in FIG. 4, will be described.

In this third embodiment, it is possible to reduce the circuit scale andarithmetic operation amount, and hence reduce power consumption, bydirectly inputting complex time waveform data, which is an IFFT outputof the IFFT circuit 103, to the P/S converting and GI adding circuit313, and omitting the IFFT circuit 112.

On the other hand, the reduction of the number of significant digitsprovided in the IFFT circuit 112 and the effect of subcarrier selectionprovided in the IFFT circuit 212 of the second embodiment is absent. Inorder to compensate for this, the P/S converting and GI adding circuit313 selects, captures and processes only higher-bit data enough for thenumber of significant digits necessary for PA control within complextime waveform data from the IFFT circuit 103, and similarly generates acomplex digital baseband signal for PA control of which the number ofsignificant bits has been reduced. As a result, it is possible to reducethe circuit scale and the arithmetic operation amount and hence reducethe power consumption as compared to when information of all complextime waveform data is input and processed.

According to the above-described third embodiment, the PA controlcircuit 314 receives complex time waveform data from the IFFT circuit103, and generates a control signal for the DC/DC converter 116 and thePA 111, so that it is possible to omit an inverse Fourier transformcalculation for obtaining complex time waveform data for PA control fromcomplex symbols. As a result, it is possible to suppress the circuitscale and the arithmetic operation amount and further suppress the powerconsumption.

Fourth Embodiment

Next, the fourth embodiment of the present invention will be described.

Although a basic configuration of this fourth embodiment is the same asthat of the first embodiment, a different technique for generating a PAcontrol signal is further provided in the fourth embodiment.

FIG. 5 is a block diagram illustrating an OFDM modulated wavetransmitter apparatus according to the fourth embodiment. Partscorresponding to FIG. 1 are denoted by the same reference numerals, anddescription thereof is omitted. In this fourth embodiment, a PA controlcircuit (control circuit) 414 and a control signal converting circuit424 are provided instead of the PA control circuit 114 and the controlsignal converting circuit 124 of the OFDM modulated wave transmitterapparatus 100 of FIG. 1, respectively.

In addition, as described below, optionally, a symbol mapping circuit401 is provided instead of the symbol mapping circuit 101, and an IFFTcircuit 412 is provided instead of the IFFT circuit 112.

Next, operations different from those of the first to third embodiments,among operations of the OFDM modulated wave transmitter apparatus 400illustrated in FIG. 5, will be described.

If subcarriers of only some frequencies in OFDM signal are often usedand particularly the repetition of uses of higher frequency subcarriersis small, it may be advantageous that a frequency band which the PAcontrol circuit 114 can follow is narrower than the entire subcarrierband because of the cost reduction using a low-speed circuit and thereduction of power consumption by a low-speed operation, when its effectis compared with the cost and power consumption of the PA controlcircuit 114 of FIG. 1.

In this fourth embodiment, on the above-described condition, the controlsignal converting circuit 424 recognizes whether or not a carrier-bandOFDM signal to be amplified by the PA 111 is within a band capable ofbeing followed by the PA control circuit 414. If the carrier-band OFDMsignal exists outside the band capable of being followed, an operationto make an output voltage of the DC/DC converter 116 follow OFDM signalamplitude stops, and a PS control signal and a PA control signal inwhich non-linear distortion of the PA 111 is lowest are output.

In the above-described ba d recognition by the control signal convertingcircuit 424, band (bandwidth) information may be input from an outsideof the OFDM modulated wave transmitter apparatus 400 to the controlsignal converting circuit 424. In addition, because the symbol mappingcircuit 401 and the IFFT circuit 412 recognizes a subcarrier band to beused, the band information may be input from the symbol mapping circuit401 and the IFFT circuit 412 to the control signal converting circuit424.

According to the above-described fourth embodiment, the band informationis input to the PA control circuit 414. Therefore, the control signalconverting circuit 424 can supply the PA 111 with power and a PA controlsignal having a predetermined voltage, regardless of a control signal byan arithmetic operation, when recognizing that a broadband OFDMmodulated wave signal, which exceeds control bands of the PA controlcircuit 414, the PA 111, and the DC/DC converter 116, is generated. As aresult, when a repetition of generation of the broadband OFDM modulatedwave signal is low, it is possible to implement cost reduction andpower-consumption reduction.

Hereinafter, advantageous effects of the above-described first to fourthembodiments will be summarized.

According to the above-described first embodiment, based on the OFDMsymbol signal, the IFFT circuit 103, the P/3 converting and GI addingcircuit 104, the timing adjusting circuit 106, the D/A converter 107,the frequency converter 108, the local oscillator 109, and the analogfilter 110 generate an OFDM modulated wave signal, and the PA controlcircuit 114, the PS 115, and the DC/DC converter 116 generate powerhaving a predetermined voltage and a PA control signal. Consequently, itts possible that each signal is generated by calculation under thenumber of significant digits suitable for the signal, so that the scaleof an arithmetic operation circuit and an arithmetic processing amountare decreased. As a result, it is possible to speed up an arithmeticoperation and reduce power consumption.

In addition, because the digital filter 121 is provided and a controlband of a control signal (a PS control signal and a PA control shrimp islimited, power consumption and circuit cost can be suppressed.

In addition, the symbol mapping circuit 101 preferentially allocates asubcarrier segment set to a multi-valued radio modulation scheme, whichis susceptible to the non-linear distortion by the amplifier, or thehigh power, which is dominant in the occurrence of non-lineardistortion, or subcarriers to be exactly used to low-frequencysubcarriers, so that an operation speed of the PA control circuit 114 isdecreased. Further, it is possible to reduce the arithmetic operationamount and configure a low-speed circuit by fixing allocation tolow-frequency subcarriers. As a result, it is possible to suppress powerconsumption and circuit cost.

Further, because the input of the PA control circuit 114 is a digitalsignal, it is possible to reduce the effect and noise or interferencefrom the environment.

In addition, according to the above-described second embodiment, it ispossible to limit the control frequency band even when there is no BPF121 because the PA control circuit 214 generates a control signal byselectively receiving a part of an OFDM symbol signal. As a result, itis possible to suppress an arithmetic operation amount and the cost ofan analog circuit and further suppress the circuit scale and powerconsumption.

In addition, according to the second embodiment, a baseband signal to beused for compensation can be generated with shifting a subcarrierfrequency to a lowest frequency. As a result, it is possible to furtherdecrease a control frequency band, reduce an arithmetic operation amountof digital processing, and introduce a low-speed analog processingsystem.

Further, according to the above-described third embodiment, the PAcontrol circuit 314 receives complex time waveform data from the IFFTcircuit 103, and generates a control signal for the DC/DC converter 116and the PA 111, so that it is possible to omit an inverse Fouriertransform calculation for obtaining complex time waveform data for PAcontrol from complex symbols. As a result, it is possible to suppressthe circuit scale and the arithmetic operation amount and furthersuppress the power consumption.

In addition, according to the above-described fourth embodiment, theband information is input to the PA control circuit 414. Therefore, itis possible to supply the PA 111 with power and a PA control signalhaving a predetermined voltage, regardless of a control signal by anarithmetic operation, when recognizing that a broadband OFDM modulatedwave signal, which exceeds control bands of the PA control circuit 414,the PA 111, and the DC/DC converter 116, is generated. As a result, whena repetition of generation of the broadband OFDM modulated wave signalis low, it is possible to implement cost reduction and power-consumptionreduction.

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2010-4135, filed Jan. 12, 2010,the entire contents of which are incorporated herein.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a broadcasting wirelesscommunication apparatus, a mobile wireless communication apparatus, asubscriber wireless communication apparatus, and a wireless local areanetwork apparatus using an OFDM scheme.

REFERENCE SYMBOLS

-   100, 200, 300, 400 OFDM modulated wave transmitter apparatus-   101, 401 Symbol mapping circuit-   102 S/P converter-   103, 112, 212, 412 IFFT circuit-   104, 113, 313 PS converting and GI adding circuit-   106, 125, 126 Timing adjusting circuit-   107 D/A converter-   108 Frequency converter-   109 Local oscillator-   110 Analog filter-   111 PA-   114, 214, 314, 414 PA control circuit (control circuit)-   115 Power supply-   116 DC/DC converter-   121 Digital filter-   122 Real component extracting circuit-   123 Amplitude detecting circuit-   124 Control signal converting circuit-   130 DFT circuit-   131 Subcarrier mapping circuit

1. An orthogonal frequency division multiplex (OFDM) modulated wavetransmitter apparatus comprising: an OFDM symbol signal generatingcircuit which generates an OFDM symbol signal from transmission data; anOFDM signal generating circuit which generates an OFDM modulated wavesignal from the OFDM symbol signal; a control circuit which generates acontrol signal from the OFDM symbol signal; and an amplifier whichamplifies and outputs the OFDM modulated wave signal generated by theOFDM signal generating circuit based on the control signal generated bythe control circuit.
 2. The OFDM modulated wave transmitter apparatusaccording to claim 1, wherein the control signal is a power amplifier(PA) control signal.
 3. The OFDM modulated wave transmitter apparatusaccording to claim 1, wherein the power amplifier further includes aconverter and a power supply, where the control signal s a power supply(PS) control signal, the converter controls an output voltage of thepower supply based on the control signal generated by the controlcircuit, and the power amplifier amplifies and outputs the OFDMmodulated wave signal based on the output voltage controlled by theconverter.
 4. The OFDM modulated wave transmitter apparatus according toclaim 1, wherein the control circuit further includes a filter forlimiting bands of the control signal.
 5. The OFDM modulated wavetransmitter apparatus according to claim 1, wherein the OFDM symbolsignal generating circuit generates an OFDM symbol signal having asubcarrier arrangement to prevent non-linear distortion from beinggenerated.
 6. The OFDM modulated wave transmitter apparatus according toclaim 1, wherein the control circuit generates the control signal frompart of the OFDM symbol signal.
 7. The OFDM modulated wave transmitterapparatus according to claim 6, wherein the control circuit includes aninverse fast Fourier transform (IFFT) circuit for bypassing acalculation path in which multiplication of 0 occurs when symbolinformation of some subcarriers is subjected to an IFFT.
 8. The OFDMmodulated wave transmitter apparatus according to claim 1, wherein: theOFDM signal generating circuit generates an OFDM baseband signal fromthe OFDM symbol signal, and generates the OFDM modulated wave signalfrom the OFDM baseband signal, and the control circuit generates thecontrol signal from the OFDM baseband signal.
 9. The OFDM modulated wavetransmitter apparatus according to claim 3, wherein: the control circuitgenerates the PS control signal from the OFDM symbol signal based onwhether or not the OFDM modulated wave signal is within a band capableof being followed, and the control circuit invalidates a control of thePS output voltage according to the converter if the OFDM symbol signalexists outside the band capable of being followed, and generates the PScontrol signal so that a preset output voltage is output from theconverter.
 10. An OFDM modulated wave transmission method comprising:generating an OFDM symbol signal from transmission data; generating anOFDM modulated wave signal from the OFDM symbol signal; generating acontrol signal from the OFDM symbol signal; controlling an outputvoltage of a power supply based on the power supply control signal; andamplifying and outputting the OFDM modulated wave signal based on thecontrol signal.
 11. A non-transitory computer readable recording mediumstoring a program for causing a computer for controlling an orthogonalfrequency division multiples (OFDM) modulated wave transmitter apparatusto execute: an OFDM symbol signal generating function of generating anOFDM symbol signal from transmission data; an OFDM signal generatingfunction of generating an OFDM modulated wave signal from the OFDMsymbol signal; a control function of generating a control signal fromthe OFDM symbol signal; a converting function of controlling an outputvoltage of a power supply based on the power supply control signal; andan amplifying function of amplifying and outputting the OFDM modulatedwave signal based on the control signal.